1. Technical Field
The invention relates to a bias controller that efficiently permits a communication device to operate in a dual mode.
2. Related Art
Communication through wireless networks has been around for some time. Initial first-generation and second-generation wireless networks were sufficient to provide air interface support for the low-rate data such as voice and text utilized by personal communication devices. However, the explosive growth of the Internet has produced a tremendous increase in the demand for wireless services that simultaneously provide several types of media formats, including streaming video, text with graphics, slides, voice, and music.
For several years, it has been widely known that existing air interfaces are inadequate to satisfy the higher data rate requirements of wireless multimedia services. Recognizing this, the International Telecommunications Union (“ITU”) in Geneva, Switzerland proposed requirements to satisfy the higher data rate needs of wireless multimedia services. An example of these requirements includes a proposed specification for third generation wireless services entitled “International Mobile Telecommunications in the year 2000” (“IMT-2000”). The ITU designed the proposed IMT-2000 specification to provide enhanced voice, data, and multimedia services over wireless networks throughout the world.
The Global System for Mobile Communications (“GSM”) is the most widely deployed second-generation (“2G”) digital mobile phone system. Generally known as the world transmission-technology leader in terms of number of subscribers, the digital GSM mode is the predominant standard in Europe. The European Standard and Technology Institute released the GSM mode standard in 1989. Businesses launched the first commercial services using the GSM mode in 1991. The CDMA (“Code Division Multiple Access”) technology is based on the interim international standard 95 (“IS-95”) protocol and is a significant 2G standard that is in operation in North America.
Under IMT-2000, a third generation (“3G”) digital mobile phone system will include the Enhanced Data Rates for GSM Evolution (“EDGE”) mode (also sometimes referred to as a “2.5G system”). The EDGE mode provides significant new air interface improvements over the GSM mode, including higher data transmission rates.
In general, the GSM mode operates as a low-rate, constant-envelope waveform, voice data transmission mode. Accordingly, a compressed amplifier may be utilized when radio frequency (“RF”) signals are input into a system operating in the GSM mode. In contrast, the EDGE mode operates as a high-rate, linear waveform, multimedia data transmission mode. Typically, a compressed amplifier may not be employed when RF signals are input into a system operating in the EDGE mode because the compressed amplifier would severally distort that input signal. CDMA, wideband CDMA, and CDMA2000 are similar to the EDGE mode of modulation in that the input signal amplitude may be modified but the signal itself may not be compressed.
The gradual change to 3G wireless networks throughout the world dictates that devices coupled to these networks improve to meet the new requirements while remaining compatible with 2G wireless networks. Accordingly, there is a need for digital communication devices to operate efficiently in a first mode compatible with a 2G system and a second mode compatible with a 3G system. In particular, there is a need for a bias controller for a power amplifier that efficiently permits a mobile phone to operate either in a compressed data transmission mode or in a linear data transmission mode.